Canada: Women in India are facing a severe problem of weight extremes with the obese getting fatter and the undernourished thinner, according to a new study that says this poses a "major challenge" to the government which should frame policies to address these health issues.

The study, "Change in the Body Mass Index Distribution for Women: Analysis of Surveys from 37 Low- and Middle-Income Countries", by the University of Toronto and the Harvard School of Public Health found that women of average weight are disappearing in India and the country sees more underweight women than obese ones.

"The study is novel because for the first time we are showing that increase in Body Mass Index (BMI) is not happening equally across the board," S. V. Subramanian, professor of Population Health and Geography at the Harvard School of Public Health, said.

"Obese and overweight people are gaining weight rapidly in low-and middle-income countries, including India, while those who are severely undernourished are not experiencing similar weight gains," said Subramanian, the senior author of the study.

"Increases in average BMI are largely driven by populations that are already overweight or obese, with little to no change among underweight individuals," he said.

The study shows a persistent problem of underweight in India, with about 25 percent of the population being underweight in 2005, and at the same time the percentage of women who are obese has doubled.

"To put this in perspective, the number of underweight women exceeds the number of overweight and obese combined in India. This pattern of persisting problems of under-nutrition along with a simultaneous rise in obesity is being seen in most of the low income countries studied," Fahad Razak, the study's lead author and a fellow at Toronto's St. Michael's Hospital, said.

Razak says underweight people die at much higher rates, perhaps because of diseases related to being malnourished, while overweight and obese people also have higher rates of death and disease, mostly from causes such as diabetes, heart disease and cancer.

"We believe that as India increases its focus on the health needs of overweight and obese people it must continue to address the needs of the large number of severely undernourished people in society," says Razak.

The study used information collected in Demographic and Health Surveys (DHS) of Indian women with a sample size of 72,469 in 1998 and 91,243 in 2005.

"One might think that as a country grows economically, the majority of the underweight population would move into the average BMI range, but our study shows the opposite and the people of average weight are disappearing in India," says Razak.

"This growing trend of body weight extremes is going to pose a major challenge for health care and policy leaders," says Razak.

"They will need to balance their priorities between addressing health issues afflicting the underweight who happen to be poor, and health issues afflicting the obese and overweight - the upper middle-class and rich."

BMI is an indicator of body fat calculated by dividing a person's weight in kilograms by their height in metres squared. Obesity is defined as having a BMI of more than 30.0 kg/m2.

Compared to people with a healthy weight (a BMI between 18.5 and 24.9 kg/m2), obese individuals and overweight individuals (who have a BMI between 25.0 and 29.9 kg/m2) have an increased risk of diabetes, heart disease and stroke, and tend to die younger.

At the same time, people who are underweight (BMI less than 18.5) also have an increased risk of death, perhaps from complications related to being malnourished.